As is known in the art, when welding tubes to tube sheets, the tubes are usually loose and slightly off center in the previously drilled holes of the tube sheet. This creates problems during the welding process, which can lead to defective welds. Repairing the defective welds adds delays and costs to the project. Tubes in tube sheets that need to be expanded either mechanically (with mechanical rollers) or hydraulically (with hydraulic expansion equipment) tend to be loose and may move out of position when inserting the expansion tooling, or during the actual expansion process. If the tube moves out of position during the process, it is difficult to reposition it and may require the tube to be removed, and a new tube installed in its place. This can cause delays and add to the cost of the project, and furthermore, can generally lead to inaccuracies in the structure of the tube sheet mounted tubes, or in any other type of structure in which the tubes have been located.
Other methods of securing tubes prior to their welding either leaves them off center, such as through pinning, or closes the gap between the tube and the tube sheet completely, such as through mechanical rolling, which traps the weld gases during the subsequent welding process, and can lead towards defective welds, and generally porosity in the weld joints. When using mechanical rollers or other tube setting devices that require the use of a lubricate to reduce friction when operating, the lubricate residue left behind must be removed prior to welding.
Furthermore, through the use of the current type of cams and segment assemblies that employ and work with polyurethane expanders, such can sometimes create a complete seal between the tube and the tube sheet, but it can trap the weld gases during the welding process. This can also provide deficiencies.
In the patent to Russell D. Wasson and David A. Vossbrinck, U.S. Pat. No. 5,901,594, issued on May 11, 1999, for High Pressure Expansion Mandrel with Cams Engaging Oppositely Directed Ends of an Expandable Segmented Ring, there is disclosed a high pressure mandrel for joining a metal tube to a wall of a metal sheet surrounding an annual bore of the metal sheet. This type of device utilizes hydraulic pressure directly within the mandrel, to provide for expansion, and exert hydraulic pressure upon the metal tube to be emplaced, in trying to set it into a permanent installation.
Other prior art patents include the patent to Kelly, U.S. Pat. No. 4,502,308, explaining a Swaging Apparatus Having Elastically Deformable Members with Segmented Supports. Therein is disclosed a swaging mandrel to be inserted into a tubular structure that is radially expandable. The shown device therein utilizes hydraulic pressure for achieving the swaging forces.
Another patent to Kelly, U.S. Pat. No. 4,414,739 shows an Apparatus for Hydraulically Forming Joints between Tubes and Tube Sheets. Once again, this discloses a mandrel, where pressurized hydraulic fluid is generated therein, that allows hydraulic fluid under pressure to enter an annular volume between the body and the interior wall of the tube, wherein it may expand the tube to provide for its seating within the tube sheet.